This invention relates generally to diaphragms for fluid pumps and in particular to high pressure fluid pump diaphragms.
High pressure pump diaphragms of the prior art have generally been fabricated from a thin disk of beryllium copper or stainless steel having a bellows type configuration about the outer periphery to allow for displacement movement of the diaphragm. The resilient characteristics of a belleville spring washer are used to create the restoring force for the electroexpansive member. It has been found, however, that for high flexure cycles, beryllium copper tends to fatigue and results in sudden breakdown. Where an electroexpansive material, such as a piezoelectric material, is used to drive a pump diaphragm it is necessary to provide a strong and low inertia restoring force to the piezoelectric material in order to achieve fast reaction time for the controlled pumping of a fluid.
The prior art devices utilizing a piezoelectric material have, at times employed a bellville spring in conjunction with a beryllium copper diaphragm which offers limited reliability because of the fatigue failure of the beryllium copper.
Other techniques for transmitting energy from the piezoelectric stack to a pump fluid include hydraulic piston arrangements in place of the beryllium copper diaphragm. As can be seen, such an arrangement, because of the mass of the piston, reduces the response time of the pumping cycle. Also, seal friction at high pump pressures reduces the force available from electroexpansive drives. In certain applications, such as, for example, a liquid chromatograph pump, the ability to flush the chamber when changing fluids is important. A smooth surface with no trapped fluid volumes is provided by the spring diaphragm of the present invention.